Karachi, Pakistan
— A stately camel, head held high, stalks across a bridge, disdaining the chaotic roar of battered taxis, swaying trucks, and lethal-looking motor-scooter rickshas pressing in from all sides on a hot Karachi morning.

Bells chink on leather straps around each lofty knee and about the curving neck. A harness connects the animal to a ramshackle wooden cart with large wheels. On the cart is stacked a pile of the world's oldest planks. On the planks perches an elderly man. On the man sits a bedraggled turban.

Dark broad-winged kites float in circles above us, hunting for food like vultures . . . a Boeing 747 in the green-and-gold of Pakistan International Airways lifts off from Karachi airport . . . women draw water from a well out on Paradise Point . . . behind them looms the shape of the nuclear power plant that supplies teeming Karachi with electricity.

Pakistan, 83 million people jammed into the northwest corner of the Indian subcontinent, now next door to Soviet troops in Afghanistan, assaults the eye and the ear with contrasts.

This is the strategic country President Reagan is trying to bolster as a counterweight to Soviet expansionism in Afghanistan. The question is how stable it is, and will be.

The situation is ironic: This is a country ruled by military generals and led by Muhammad Zia ul-Haq. India is the world's largest democracy. In a more ordered world, Moscow would support the dictatorship, the United States the democracy. In fact, it is exactly the other way around.

''Never forget, this is a Western country,'' says a senior Pakistani diplomat. Indeed, Pakistanis I talked to spoke often of relatives and friends in the US. The editor of the English-language Pakistan Times in Rawalpindi, Z. A. Suleri, has written a long series of impressions about the US after a recent visit to his daughter at Williams College in Massachusetts. A businessman also had children studying in the US.

Pakistan's armed forces have traditionally been equipped with US and French weaponry.

President Zia's critics, however, say he only wants more US arms (a $3.2 billion economic and military sales credit package has been moving through Congress) to bolster his defenses against India. Official spokesmen insist otherwise. They stress the dangers of lightning air attacks from Afghanistan by Soviet-trained pilots (or Soviet pilots in Afghan uniforms).

The only Russians visible here are the 1,400 men assigned to build and operate Pakistan's first steel mill, outside Karachi. ''Most of them are looking for espionage,'' sniffed one businessman. ''We know that. But we need the mill. . . .

''You know, we Pakistanis are free traders, capitalists if you like.''

Men like this are divided about President Zia and the generals.

On the one hand, they tell you over long dinners in their comfortably furnished homes that Zia is developing industry and stressing Islamic morality. They like that.

On the other, they fret. Capitalism, the source of their own wealth, can flourish only in a democracy, they firmly believe. Zia took power in 1977 saying it was only for 90 days. He is still in the quiet and tree-lined capital of Islamabad, to the north.

''Zia's title is CMLA - chief martial law administrator,'' said a successful Karachi entrepreneur with a grin. ''People have another way of using those initials: Cancel my latest announcement.''

Zia appears reasonably safe in office for a while, at least, many people believe. In part it's because the economy is doing well: good crops, a growth rate of 5.7 percent last year, plenty of money to go around, an inflation rate of 12 to 13 percent.

Opposition political parties are divided, and harassed by police. Leaders are arrested every now and then. Zia shows little sign of agreeing to the latest demands of eight of the parties: talks on the future in return for an end to press censorship, release of political prisoners, and lifting the ban on political activity.

The tall, white National Assembly building in Islamabad remains empty. Government officials are billeted in the hostels that once housed members of the Assembly in town for legislative sessions. Zia talks of creating a new bicameral legislature. No one holds his breath in anticipation.

''I want democracy to return,'' a businessman says. ''But sometimes I wonder if we're ready for it. I mean, look at the mess (Zulfikar Ali) Bhutto made of things. . . .'' Mr. Bhutto, the previous president, was executed by Zia.

Corruption, usually found in developing countries racing to build a modern world on ancient poverty, seems to be rampant in Pakistan. Letters to the editor in the heavily censored press cite chapter and verse as officials try to take sporadic action.

''It's the generals and the senior officers who are raking it in,'' a Western diplomat says privately. ''Take a look at how many retired officers head business companies. It's a patronage system to reward service and head off complaints.''

Visitors returned from Peshawar, to the northwest, tell of luxurious life styles for generals. They live in former British cantonments. Army trucks take children to school. Officers shop for duty-free goods on frequent jaunts to the Gulf states. Late-model cars abound.

People seem to know it - and to shrug. Smuggling in consumer goods from TV sets to videotape recorders to cars is commonplace. The border city of Bara is widely known for it: The smugglers' bazaar in Rawalpindi is known as ''mini Bara.''

''I was asked for 20,000 rupees (about $2,000) as a bribe to have my telephone and telex shifted to a new building,'' one businessman said. ''Fortunately, I knew some influential people and I didn't have to pay in the end. If you don't have contacts, you pay.''

He smiled. ''We say that corruption has been nationalized now. . . .''

''We think America should think twice before committing itself too heavily to Zia,'' another Pakistani commented. ''What will you do if he is replaced by someone like Benazir (Bhutto, daughter of the former president, now in jail while her brother leads an exile opposition group from Kabul, Afghanistan)? Many people would vote for her. But why would a person like her even talk to you after the way you've backed Zia?''

One answer is that any new Pakistani ruler hasn't much of a choice: People here don't like Moscow. They fear and distrust India. But even staunch friends of the US want the US to help Pakistan, but the Pakistanis want to retain control of US weapons. They want flexibility and stability over the long term - an American presence that stays and won't be rejected when the country one day returns to democracy.

Meanwhile, Karachi streets are an endless stream of curious vehicles and donkey- and camel-drawn carts. Local trucks have high wooden sides, painted with garish scenes of animals, birds, mountains, and lakes. Zia has outlawed such decorations in the name of Islam, but they persist - along with elaborately worked tin strips around fender edges and along hoods.

Private minibuses are a blaze of multicolored paint by day, and they are happily lit up with colored lights by night, like mobile Christmas trees.

Motor-scooter rickshas careen in and out, several people jammed into the two seats at the back. Jeeps carry 10 or more laughing men. Women are swathed in Islamic black. It's a man's world. It is Zia's world - for how long?